Valve arrangement for controlling hydraulic fluid in an axial piston machine

ABSTRACT

In the stationary part ( 1 ) of an axial piston machine, a first flow duct ( 2 ) and second flow duct ( 5 ) intersect with the central axes ( 3 ) and ( 6 ). A valve body ( 20 ) having a valve cone ( 21 ) and a tubular guide piston which can be displaced in relation to the valve cone is situated in the extension of the central axis ( 3 ) of the first flow duct ( 2 ). The valve body ( 21 ) bears against a first valve seat ( 4 ) which is surrounded by an expanded section ( 7 ). The entire valve body ( 20 ) moves in a tubular partial housing ( 9 ) which is connected to the stationary part ( 1 ) in a sealed manner via a seal ( 11 ), a screw connection ( 10 ) and a flange ( 12 ) which rests on a shoulder ( 13 ) of the stationary part ( 1 ). A first compression spring ( 27 ) and a second compression spring ( 28 ) serve to support the valve body ( 20 ) and its parts in relation to one another. An extension stem ( 22 ) passes through the tubular guide piston and guides the second compression spring ( 28 ). The tubular partial housing ( 9 ) sits in a bore ( 8 ) of the stationary part ( 1 ). Two valves V 1  and V 2  are formed, the valves setting flow paths between the first flow duct ( 2 ) and the second flow duct ( 5 ) which differ according to pressure ratios.

BACKGROUND OF THE INVENTION

The invention relates to a valve arrangement for controlling hydraulicfluid in an axial piston machine in which a first flow duct is providedin a stationary part and opens out into a second flow duct runningtransversely, an accommodating space of the stationary part being formedlying opposite the second flow duct in the extension of the first flowduct and being intended for accommodating and guiding a multiple valvebody, which can be displaced in the direction of the central axis of theflow duct and in which the multiple valve body comprises a first and asecond valve body which are arranged one behind the other in thedirection of the longitudinal axis of the first flow duct and can bedisplaced in relation to each other in this direction.

A valve arrangement of this type has frequently been fitted in variousaxial piston machines. The valve PLC 182 on page 6-9-3 of publicationHY17-8702/UK of February 2001 by Parker Mobile Hydraulics is one suchexample. In this case, the first flow duct is connected to a hydraulicfluid store which is under low pressure, i.e. it serves as a feed-inline. The second flow duct of the known valve arrangement serves as aconnecting line to a high-pressure working line, and can therefore beunder high pressure or low pressure depending on the operatingconditions. The two valve bodies, together with associated valve seatsform a first and a second valve, one serving as a feed valve andenabling hydraulic fluid which is under low pressure to flow from thefirst flow duct into the second flow duct. By contrast, the other valveserves as a pressure-limiting valve and enables hydraulic fluid to flowfrom the connecting line into the feed line if the working pressure inthe high-pressure working line has become impermissibly high.

The known valve arrangement is therefore a directly controlled, presethigh-pressure limiting valve with a feed-in function. In terms ofstructure, it is designed in such a manner that the first valve body isinserted into the second valve body where it has its valve seat, whilethe second valve body interacts with a seat formed in the stationarypart. Two valves are therefore fitted one inside the other, the twovalve seats being spaced apart only a little distance from each other inthe direction of the central axis of the first flow duct. In this knownvalve arrangement, the through flow cross section is thereforerestricted for structural reasons. This is true with a pressure-limitingvalve because the valve serving for this purpose has to be arrangedwithin the cross section of the valve body that implements the feed-infunction.

However, it is precisely for the pressure-limiting function that a rapidresponse is imperative, for which purpose relatively large flow crosssections are desired. In order to satisfy this demand, the known valvearrangement would have to be designed with very large cross sections.However, this is not possible when it is fitted into axial pistonmachines.

Pilot-controlled valves are therefore generally used in cases of thistype. One example of this is illustrated and described in DE 102 39 725A1. According to this, a hydraulic pressure-limiting valve has a firstflow duct and a second flow duct running transversely with respect toit. This pressure-limiting valve permits hydraulic fluid to pass fromthe first flow duct into the second flow duct if the pressure of thehydraulic fluid in the first flow duct exceeds a certain thresholdvalue. For this purpose, a first valve body is arranged in the regionbetween the two flow ducts. The first valve body is bored through, sothat the first flow duct is connected continuously to the space behindthe first valve body. A second valve is arranged behind the first valvebody, coaxially with it, and serves as a pilot valve. If the pressure ofthe hydraulic fluid in the first flow duct exceeds a threshold value,the pilot valve opens. In conjunction with a correctly dimensionedrestoring spring, the effect achieved by the dropping pressure on therear side of the first valve body is that the opening and closing forcesfor the first valve body are reduced. However, the larger a valve is,the more expensive it is to produce and to use. Pilot-controlled valvesare always more expensive than directly controlled valves. In addition,they have to be designed such that they can be adjusted because theycannot be preset with sufficient accuracy.

It is therefore a primary object of the present invention to provide avalve arrangement of the type mentioned, which permits largethroughflows with a low pressure loss, takes up little installationspace and can be produced cost-effectively.

These and other objects will be apparent to those skilled in the art.

BRIEF SUMMARY OF THE INVENTION

A valve arrangement is provided for controlling hydraulic fluid in anaxial piston machine in which a first flow duct (2) is provided in astationary part (1) and opens out into a second flow duct (5) runningtransversely with respect to it, having the following features:

-   -   a) an accommodating space (14) of the stationary part (1) is        formed, lying opposite the second flow duct (5), in the        extension of the first flow duct (2) and is intended for        accommodating and guiding a multiple valve body (20), which can        be displaced in the direction of the central axis (3) of the        first flow duct (2);    -   b) the multiple valve body comprises a first, and a second valve        body which are arranged one behind the other in the direction of        the longitudinal axis of the first flow duct (2) and can be        displaced in relation to each other in this direction;    -   c) the first valve body facing the first flow duct (2)        interacts, in order to form a first valve (V1), with a first        valve seat (4) which is formed in the region in which the first        flow duct (2) opens out into the second flow duct (5);    -   d) the second valve body interacts, in order to form a second        valve (V2), with a second valve seat (29) which is formed in the        first valve body and is situated in the region of the second        flow duct (5), the hydraulic cross section F₂ of the second        valve seat (29) being larger than the hydraulic cross section F₃        of the first valve seat (4) and the two valve bodies being        prestressed against their valve seats (4, 29) by compression        springs (27, 28);    -   e) the accommodating space (14) of the stationary part (1) is        connected to the first flow duct (2) via the two valve bodies,        but is sealed off from the second flow duct (5);    -   f) the hydraulically effective cross sections F₂ and F₃ of the        first and second valve seat (4, 29) are dimensioned in such a        manner and the two compression springs (27, 28) are coordinated        in such a manner that    -   f1) the first valve (vi) opens when the 30 hydraulic fluid in        the second flow duct (5) has a pressure P₅ which is larger than        the pressure P₂ in the first flow duct (2) and the threshold        value is exceeded, or    -   f2) the second valve (V2) opens when the hydraulic fluid in the        first flow duct (2) has a pressure P₂ which is greater than the        pressure P₅ in the second flow duct (5) and a threshold value is        exceeded, while    -   f3) in the inoperative position the two valves (V1, V2) are        closed.

In the case of the valve arrangement according to the invention, thesecond valve seat, which is formed between the two valve bodies, issituated in the region of the second flow duct, as a result of which itshydraulic cross section can be considerably larger than the valve seatof the first valve, which seat is formed in the region in which thefirst flow duct opens out into the second flow duct, and therefore onthe stationary part. The two valve seats move apart to a certain extentand are controlled in mutual dependence via their diameter and arearatios. In contrast to the prior art, there are not two individualvalves fitted one inside the other, in the case of the valve arrangementaccording to the invention, but rather a valve system having an overallcontrol, it being of particular importance that the accommodating spaceof the stationary part is connected to the first flow duct via the twovalve bodies, but sealed off from the second flow duct. The thresholdvalue for the two valves is determined by the two compression springs.

The valve arrangement according to the invention therefore permits largethrough flows with a low pressure loss, is a very compact constructionand nevertheless manages with few individual parts, and so it can beproduced economically.

The valve arrangement according to the invention is advantageouslyprovided in an axial piston machine having a hydraulic control, in whichthe first flow duct serves as a connecting line to a high-pressureworking line and the second flow duct serves as a connecting line to asource for hydraulic fluid which is under high pressure, the first valvebeing operated as a feed valve and the second valve being operated as apressure-limiting valve.

In this arrangement, a large transition cross section from the firstflow duct into the second flow duct is available particularly for thepressure-limiting function in the working line, i.e. the “high-pressurefunction”.

Claims 3 to 5 therefore contain structural details, such as threedifferent hydraulic cross sections F₁, F₂ and F₃ which determine thecontrol of the valve arrangement. A decisive factor in every case isthat the hydraulic fluid present in the first flow duct passes into theaccommodating space of the stationary part where it fills all of thecross sections and, by differently pressurizing the tubular guide pistonand the valve cone, depending on the operating state, triggers adifferent opening function.

The guiding of the first and of the second valve cones on each other isthe subject matter of Claims 6 to 8. For easy assembly, the valve coneand its extension stem 22 namely have to be produced separately and puttogether only after the second compression spring is fitted. Theconnection takes place on the hollow guide stem 25 which is formed onthe valve cone. In this case, the extension stem is introduced into theguide stem and, in principle, can be connected in different ways, suchas a press fit, soldering, welding or bonding. However, the screwconnection which is specified by claim 7 is preferred because it opensup the possibility of also setting the spring prestress simultaneouslywith the connection. In this case, a different depth of penetration ofthe fastening thread is possible, but similarly also the interpositionof spacer discs.

The design and accommodation of the compression springs specified inClaims 8 to 12 results in the already mentioned, particularly compactconstruction of the valve arrangement according to the invention.

The arrangement of a special, tubular partial housing according to Claim12 facilitates the assembly and permits relatively great structuralfreedom in designing the accommodating space for accommodating andguiding the second valve body.

Claims 13 and 14 show one structural possibility of how the first flowduct can be brought permanently into connection with the accommodatingspace of the stationary part, in which case interior spaces in thetubular guide piston also have to be filled with the hydraulic fluidoriginating from the first flow duct. However, the flow passage claimedby Claim 14 is in no way the sole possibility for this. It is alsopossible for the play between the outer circumferences of the valvecone, its guide stem and the pressure and guide plate in relation to thesurrounding inner walls of the tubular guide piston to bring about thisconnection in a specific manner if the sealing cone is open on its endsurface facing the first flow duct and therefore permits hydraulic fluidto reach the outer circumferences mentioned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal section through the valve arrangementaccording to the invention, with the two valves being in the closedstate;

FIG. 2 shows details of FIG. 1 on an enlarged scale;

FIG. 3 is an illustration corresponding to FIG. 1, and shows the feed-infunction, but in which the first valve V1 is open;

FIG. 4 constitutes the illustration corresponding to FIG. 2 duringopening of the second valve V2, and shows the high-pressure function;and

FIG. 5 shows structural modifications of details of the valvearrangement according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 schematically illustrates a stationary part which is situated onan axial piston machine. It may also be fitted in the interior of theaxial piston machine. A first flow duct 2, the central axis of which isdesignated by 3, opens out into the stationary part 1. A second flowduct 5 having the central axis 6 runs transversely thereto. The firstflow duct 2 opens out into the second flow duct 5. At the point at whichthe first flow duct 2 opens out into the second flow duct 5, a firstvalve seat 4 is formed in the stationary part 1. In this case, the firstflow duct 2 is provided at its opening-out end with an expanded section7 which surrounds the valve cone 21, which is to be described later. Asa consequence of this expansion, there is essentially only linearcontact between the valve cone 21 and the valve seat 4.

In the extension of the first valve duct 2, a bore 8 having the samecentral axis 3 as the first flow duct 2 is situated in the stationarypart 1. A tubular partial housing 9 is inserted in a pressure tightmanner into this bore. The partial housing 9 is connected to thestationary part 1 via a screw connection 10, sealed by a flange 12 on arecessed shoulder 13 of the stationary part 1 and sealed at its endprotruding into the second flow duct 5 by additional seals 11. Thetubular partial housing 9 is closed on its outside.

The bore of the tubular partial housing 9 forms an accommodating space14 and a cylindrical guide for a tubular guide piston 15. The latterforms part of a multiple valve body 20, which comprises a first and asecond valve body. The first valve body is a valve cone 21, while thetubular guide piston 15 is the second valve body. At its end facing thefirst flow duct 2, the guide piston 15 has an end wall 16 of relativelysolid design, while its remaining region 15 a, i.e. most of its length,is designed as a cylindrical tube. The end wall 16 inwardly forms aninner shoulder 17 and is provided with a bore 18. Annular grooves 19ensure that although the tubular guide piston 15 can slide in the bore14 of the tubular partial housing 9, a passage of hydraulic fluid fromthe second flow duct 5 into the interior of the partial housing 9 isprevented.

The valve cone 21 is arranged in a longitudinally displaceable manner onthe tubular guide piston 15. Particular importance is attached to theshape of the valve cone 21. FIG. 1 clearly shows that the valve cone 21is basically annular in the form of a conical annular casing 21 a, theconical annular casing expanding in the direction of the transition fromthe first flow duct 2 into the second flow duct 5. By means of its outercontour, which is at the bottom in FIG. 1, the valve cone 21 interactswith the first valve seat 4. In the interior, the valve cone 21 is,however, broken through and is provided with a ribbed structure 23 andopenings 24.

At its end facing away from the first valve seat 4, the valve cone 21 isprovided with a hollow guide stem 25. The connection of the hollow guidestem 25 to the conical annular casing 21 a takes place via the ribbedstructure 23. The hollow guide stem 25 engages in the bore 18 of the endwall 16 which is formed on the tubular guide piston 15. As a result, thevalve cone 21 and the tubular guide piston 15 can be displacedlongitudinally in relation to each other.

An extension stem 22 engages in the interior of the hollow guide stem 25and is connected at this point releasably and adjustably by means of athread to the valve cone 21. At that end of the extension stem 22 whichfaces away from the valve cone 21, a pressure and guide plate 26 isformed. The latter has three functional surfaces, namely an outersurface 26 a, an inner, annular surface 26 b facing the valve cone 21,and a circular cylindrical circumferential surface 26 c. The outersurface 26 a is acted upon by a first compression spring 27, which issupported at its opposite end on the closing-off, outer end wall of thetubular partial housing 9.

The inner annular surface 26 b forms a stop and active surface for asecond compression spring 28. The second compression spring 28 acts atits opposite end on the inner shoulder 17 (already mentioned) of thetubular guide piston 15. The two compression springs 27 and 28 aredesigned as helical springs.

It is now clear that the prestress of the two compression springs 27, 28can be influenced by the screw connection between the extension stem 22and the hollow guide stem 25. It is also possible in this case forspacer discs to be pushed onto the extension stem, for example before itis screwed together with the valve cone 21.

In the assembled state, there remains an annular cylindrical inner space15 b, in which the second compression spring 28 is situated, between theinner wall of the tubular guide piston 15 and the extension stem 22. Inthe assembled state, the first compression spring 27 is furthermoreprestressed and presses the valve body 20, and therefore also the valvecone 21, against the first valve seat 4. As a result, the valve seat 4and valve cone 21 form a first valve V1.

A second valve V2 is formed by the valve cone 21 at its larger endfacing away from the first valve seat 4, itself being designed as avalve seat 29. This is the second valve seat of the arrangement. Itinteracts with the end wall 16 (already mentioned) of the tubular guidepiston 15. For this purpose, the end wall 16, at its outer end facingthe valve cone 21, has the shape of a collar 30 of slightly enlargeddiameter. It has to be ascertained that the second valve seat 29 issituated centrally in the cross section of the second flow duct 5. Thecollar 30 can therefore be acted upon on both of its sides by thepressures prevailing in the flow ducts.

The definitive diameters are emphasized in the enlarged illustrationaccording to FIG. 2. In this case, d₁ is the diameter which the tubularguide piston has over most of its length. The outside diameter of thecollar 30, which is situated on the end wall 16 of the tubular guidepiston 15, is designated by d₂. The inside diameter of the first flowduct 2 in the region of the first valve seat 4 is designated by d₃.Definitive flow cross sections F₁, F₂ and F₃ correspond to the diametersd₁, d₂ and d₃, as will be explained in greater detail below.

The collar 30 forms, together with the second valve seat 29, the secondvalve V2.

In that end region which is connected to the hollow guide stem 25, theextension stem 22 is open on the end side and is provided with a flowpassage 31. The latter is composed of a longitudinal bore 32 and atransverse bore 33. As a result, a flow connection for the hydraulicfluid between the first flow duct 2 and the annular cylindrical interiorspace 15 b in the tubular guide piston 15 is produced via the ribbedstructure 23 of the valve cone 21.

Between the circular cylindrical circumferential surface 26 c of thepressure and guide plate 26 and the inside diameter of the tubular guidepiston 15 there is play of sufficient size, so that a flow connection isprovided between the annular cylindrical interior space 15 b and theinterior space of the tubular partial housing 9, in which the firstcompression spring 27 is situated. As an alternative, the longitudinalbore 32 in the extension stem 22 may also be continued into the outersurface 26 a of the pressure and guide plate 26. A decisive factor isthe bringing about of a continuous interior space comprising theinterior spaces of the valve cone, the tubular guide piston 15 and thetubular partial housing 9. This continuous interior space iscontinuously connected to the first guide duct 2 but, when the valves V1and V2 are closed, is adequately sealed off from the second flow duct 5.The sealing takes place by means of the annular grooves 19 (alreadymentioned) between the region 15 a of the tubular guide piston 15 andthe inner wall of the accommodating space 14 in the tubular partialhousing 9.

In addition, the play between the circular cylindrical circumferentialsurface 26 c of the pressure and guide plate 26 and the inside diameterof the tubular guide piston 15 is decisive for the damping of the valve.If the flow connection between the interior of the valve cone 21 and theaccommodating space 14 of the tubular partial housing 9 is produced viaa continuous duct in the extension stem 22, then the play which ismentioned can be focused solely on the damping requirements.

The manner of operation of the valve arrangement illustrated in FIGS. 1to 4 is described below.

The state according to FIGS. 1 and 2 arises when the difference inpressure of the hydraulic fluid in the two flow ducts 2 and 5 does notexceed a threshold value. The threshold value of the first valve V1 isdetermined by the first compression spring 27 and the threshold value ofthe second valve V2 is determined by the second compression spring 28.The two compression springs 27 and 28 then have the effect of the twovalves V1 and V2 remaining closed.

P₂ designates the pressure in the first flow duct 2 and P₅ designatesthe pressure in the second flow duct. In the event of P₅ being greaterthan P₂ and the difference in pressure exceeding the threshold value, anactuating force (P₅-P₂) (F₁-F₃) arises. This is because the pressureacting externally on the unit comprising the valve cone 21 and tubularpiston 15 is eliminated as far as the diameter d₁ in both directions ofactuation, while in the cross-sectional region d₂ to d₁ the lowerpressure P₂ prevailing on the inside opposes the higher pressure P₅prevailing on the outside. This difference in pressure has the effect oflifting off the valve cone 21, and therefore also the tubular piston 15,from the first valve seat 4, with the first valve spring 27 beingcompressed. The first valve V1 therefore opens. This state isillustrated in FIG. 3. The hydraulic fluid which is under the higherpressure Ps then flows out of the second flow duct 5 into the first flowduct 2 until the pressure is equalized, the threshold value is droppedbelow and the valve V1 closes again.

By contrast, if P₂ is greater than P₅ and the threshold value isexceeded, then the valve cone 21 is held against the first valve seat 4because the pressure P₂ acting in the direction of the valve seat 4 actson the larger surface and the pressure P₂ acting in the oppositedirection can act only on the surface. By contrast, the actuating force(P₂-P₅) (F₂-F₁) comes about on the collar 30 of the tubular guide piston15. This is because the compressive forces (at the top and bottom in thedrawing) acting on the two end surfaces of the tubular guide piston 15are compensated for up to the diameter d₁, but in the region of thecollar 30, i.e. between d₁ and d₂, the lower pressure P₅ on the outsideopposes the greater pressure P₂ on the inside. In consequence, thetubular guide piston 15 lifts off from the second valve seat 29, and thesecond valve V2 opens, cf. FIG. 4. In this case, hydraulic fluid flowsout of the first flow duct 2 into the second flow duct 5 until thepressure is equalized, the threshold value is dropped below and thesecond valve V2 is closed again.

FIG. 5 is an illustration of the partial housing 9 with the tubularguide piston 15 and the valve cone 21, with some details having beenmodified in comparison with the first exemplary embodiment. The partsare basically the same as in the first exemplary embodiment, and so thereference numbers which have already been introduced have been able toremain unchanged for this too.

The support of the first compression spring 27 has been changed.According to FIG. 5, the first compression spring 27 is no longersupported on the outer surface 26 a of the pressure and guide plate 26which is situated on the extension stem 22. On the contrary, the firstcompression spring 27 acts on the end surface 15 c of the cylindricalregion 15 a of the tubular guide piston 15. There are therefore nochanges to the entire characteristics of the valve arrangement accordingto the invention because the valve cone 21 and the tubular guide piston15 are in any case pressed against each other by the second compressionspring 28 which has to be considerably stronger than the firstcompression spring 27.

Furthermore, in the case of the exemplary embodiment according to FIG.5, a flow passage having a longitudinal bore and transverse bore in theextension stem 22 has been omitted.

According to FIG. 5, the collar 30 on the end wall 16 of the tubularguide piston 15 is pulled a good distance downwards and therefore formsa guide sleeve for the valve cone 21 which is largely situated in theinterior of the sleeve-shaped collar 30. In this variant, the collar 30engages over the sealing surface on the valve cone 21. That region ofthe valve cone 21 which is at the bottom in FIG. 5, as before, forms,together with a valve seat, which is formed on the stationary part, thefirst valve. The hydraulic fluid which is situated in the first flowduct enters via the end-side opening 35 into the valve cone 21 andpasses via a transverse bore 36, formed in the valve cone 21, and viathe radial play between the valve cone and the interior space of thecollar 30 into an annular space which is formed in the transition fromthe valve cone 21 to the hollow guide stem 25. The hydraulic fluid thenpasses via an inlet cone 37 in the end wall 16 of the tubular guidepiston 15 and via an adequately dimensioned radial play 38 between thehollow guide stem 25 and the end wall 16 into the inner annular spacebetween the cylindrical region 15 a of the tubular guide piston and theextension stem 22. The connection between the extension stem 22 and thevalve cone 21 also takes place here by a fastening thread 34 which hasbeen supplemented by a centering pin 39.

A decisive factor here is also that a connection from the first flowduct to the accommodating space 14 for the tubular guide piston 15 isalways ensured.

1. A valve arrangement for controlling hydraulic fluid in an axialpiston machine, in which a first flow duct (2) is provided in astationary part (1) and opens out into a second flow duct (5) runningtransversely with respect to it, comprising: an accommodating space (14)of the stationary part (1) lying opposite the second flow duct (5) inthe extension of the first flow duct (2) for accommodating and guiding amultiple valve body (20), which is displaced in the direction of thecentral axis (3) of the first flow duct (2); the multiple valve bodyhaving a first and a second valve body which are arranged one behind theother in the direction of the longitudinal axis of the first flow duct(2) and are displaced in relation to each other in this direction; thefirst valve body facing the first flow duct (2) engaging with a firstvalve seat (4) formed in the region in which the first flow duct (2)opens out into the second flow duct (5) to form a first valve (V1); thesecond valve body engaging with a second valve seat (29) formed in thefirst valve body and situated in the region of the second flow duct (5)to form a second valve (V2), the hydraulic cross section F₂ of thesecond valve seat (29) being larger than the hydraulic cross section F₃of the first valve seat (4) and the two valve bodies being prestressedagainst their valve seats (4, 29) by first and second compressionsprings (27, 28); the accommodating space (14) of the stationary part(1) being connected to the first flow duct (2) via the two valve bodiesand sealed from the second flow duct (5); and the hydraulicallyeffective cross sections F₂ and F₃ of the first and second valve seat(4, 29) having dimensioned and the two compression springs (27, 28)being coordinated such that the first valve (V1) opens when thehydraulic fluid in the second flow duct (5) has a pressure P₅ which islarger than the pressure P₂ in the first flow duct (2) and the thresholdvalue is exceeded, or the second valve (V2) opens when the hydraulicfluid in the first flow duct (2) has a pressure P₂ which is greater thanthe pressure P₅ in the second flow duct (5) and a threshold value isexceeded, while in the inoperative position the two valves (V1, V2) areclosed.
 2. The device of claim 1 wherein the first flow duct (2) servesas a connecting line to a high-pressure working line and the second flowduct (5) serves as a connecting line to a source for hydraulic fluidthat is under high pressure, the first valve (V1) being operated as ahigh-pressure feed valve and the second valve (V2) being operated as apressure-limiting valve.
 3. The device of claim 1 wherein the firstvalve body is a valve cone (21) with an extension stem (22) positionedat its end opposite the first valve seat (4); the second valve bodyhaving the shape of a tubular guide piston (15) guided in alongitudinally displaceable manner in the accommodating space (14) ofthe stationary part (1) for accommodating and guiding the first valvebody; the first compression spring (27) being supported on thestationary part (1) and prestressing the multiple valve body against thefirst valve seat (4); the second valve spring (28) positioned betweenthe tubular guide piston (15) and the valve cone (21) and prestressingthe guide piston (15) against the second valve seat (29).
 4. The deviceof claim 3 wherein an end wall (16) of the tubular guide piston (15)1interacts with the second valve seat (29) and has an outer collar (30),the outside diameter d₂ of which is enlarged in comparison with theoutside diameter d₁, of the remaining region (15 a) of the tubular guidepiston (15) and, in the closed state of the second valve (V2), bearsagainst the second valve seat (29).
 5. The device of claim 4 wherein theoutside diameter d₂ of the collar (30), the outside diameter d₁ of theremaining region (15 a) of the tubular guide piston (15), and thehydraulically effective diameter d₃ of the first valve (V1) determinethe hydraulically effective cross sections F₁, F₂ and F₃ of the valvearrangement, which are graduated in accordance with the relationshipF₂>F₁>F₃.
 6. The device of claim 5 wherein a guide stem (25) ispositioned at the end of the valve cone (21) facing away from the firstvalve seat (4), said guide stem being guided in a slideable manner in abore (18) in the end wall (16) of the tubular piston (15).
 7. The deviceof claim 6 wherein the extension stem (22) is screwed into the guidestem (25) which is hollow and has an internal thread.
 8. The device ofclaim 7 wherein the tubular guide piston (15) surrounds the extensionstem (22) at a distance, and the second compression spring (28), whichis supported under prestress on stop and active surfaces of the guidepiston (15) and of the extension stem (22), is arranged in the annularcylindrical interior space (15 b) between the guide piston (15) and theextension stem (22).
 9. The device of claim 8 wherein a pressure andguide plate (26) is secured to the end of the extension stem (22) facingaway from the valve cone (21), the pressure and guide plate (26), on itsinner annular surface (26 b) facing the valve cone, serving as a stopand active surface for the second compression spring (28) and, on itscircular cylindrical circumferential surface (26 c), being guided in aslideable manner in the tubular guide piston (15).
 10. The device ofclaim 9 wherein the pressure and guide plate (26) is acted upon itsouter surface (26 a) facing away from the valve cone (21) by the firstcompression spring (27).
 11. The device of claim 9 wherein the firstcompression spring (27), which is supported in a stationary manner, actsupon the tubular guide piston (15) on its end surface (15 c) which facesoutwards and faces away from the valve seats (4, 29).
 12. The device ofclaim 11 wherein a tubular partial housing (9), which is inserted fromthe outside in a pressure tight manner into the stationary part (1), isdesigned in its interior as an accommodating space (14) and guide of thetubular guide piston (15) and serves to support the first compressionspring (27) on the stationary part (1).
 13. The device of claim 12wherein the valve cone (21) is connected in the form of an annularcasing (21 a) via a ribbed structure (23) to the hollow guide stem (25).14. The device of claim 13 wherein the end of the extension stem (22)which is inserted into the hollow guide stem (25) is open on the endside and is connected via a flow passage (31), which is formed in itsinterior, to the annular cylindrical interior space (15 b) of thetubular guide piston (5), as a result of which the connection to thefirst flow duct (2) is also formed via the ribbed structure (23) of thevalve cone (21).